Array Deletion at End in DSA C# - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after deleting the last element from the array?

Consider the following C# code that deletes the last element from an array by creating a new smaller array. What will be printed?

DSA C#

int[] arr = {10, 20, 30, 40, 50};
int n = arr.Length;
int[] newArr = new int[n - 1];
for (int i = 0; i < n - 1; i++)
{
    newArr[i] = arr[i];
}
foreach (int val in newArr)
{
    Console.Write(val + " ");
}

A 20 30 40 50

B 10 20 30 40 50

C 10 20 30 40

D 10 20 30 50

💡 Hint

The new array has one less element, copying all except the last.

The code copies all elements except the last one (index n-1) into newArr, so the output is the first four elements.

❓ Predict Output

intermediate

What happens if we try to delete the last element from an empty array?

Given this C# code snippet, what will happen when it runs?

DSA C#

int[] arr = {};
int n = arr.Length;
int[] newArr = new int[n - 1];
for (int i = 0; i < n - 1; i++)
{
    newArr[i] = arr[i];
}
Console.WriteLine(newArr.Length);

A 0

B Throws ArgumentOutOfRangeException

C Throws System.IndexOutOfRangeException

D Throws OverflowException

💡 Hint

Array size cannot be negative.

The code tries to create an array with size n-1 = -1, which is invalid and throws an exception.

🔧 Debug

advanced

Why does this code throw an exception when deleting the last element?

Analyze the code below. It aims to delete the last element from an array but throws an exception. What is the cause?

DSA C#

int[] arr = {1, 2, 3};
int n = arr.Length;
int[] newArr = new int[n];
for (int i = 0; i < n - 1; i++)
{
    newArr[i] = arr[i];
}
Console.WriteLine(newArr[n - 1]);

A No exception; output is 0 because last element is default int value

B The newArr size is not reduced, so last element is default 0, no exception

C Accessing newArr[n - 1] which is uninitialized causes NullReferenceException

D ArrayIndexOutOfBoundsException due to loop condition

💡 Hint

Check array size and initialization of elements.

The newArr has same size as arr but last element is not assigned, so it defaults to 0. No exception occurs; output is 0.

🧠 Conceptual

advanced

What is the time complexity of deleting the last element from a fixed-size array by copying?

If you delete the last element from an array by creating a new array and copying all elements except the last, what is the time complexity?

A O(n) - linear time

B O(1) - constant time

C O(log n) - logarithmic time

D O(n^2) - quadratic time

💡 Hint

Consider how many elements are copied.

Copying n-1 elements requires time proportional to n, so complexity is O(n).

🚀 Application

expert

After deleting the last element from this array, what is the printed output?

Given the code below, what will be printed?

DSA C#

int[] arr = {5, 10, 15, 20, 25};
int n = arr.Length;
int[] newArr = new int[n - 1];
Array.Copy(arr, newArr, n - 1);
for (int i = 0; i < newArr.Length; i++)
{
    Console.Write(newArr[i] + " -> ");
}
Console.Write("null");

A 5 -> 10 -> 15 -> 25 -> null

B 5 -> 10 -> 15 -> 20 -> 25 -> null

C 10 -> 15 -> 20 -> 25 -> null

D 5 -> 10 -> 15 -> 20 -> null

💡 Hint

Array.Copy copies specified number of elements from source to destination.

Array.Copy copies first n-1 elements (5 elements - 1 = 4) from arr to newArr, so last element 25 is excluded.

Practice

1. What happens when you delete an element from the end of an array in C#?

easy

A. The array size remains the same but the last element is set to zero.

B. The first element is removed and the array size decreases by one.

C. All elements are shifted to the right.

D. The last element is removed and the array size decreases by one.

Solution

1. Step 1: Understand array deletion at end

   Deleting at the end means removing the last element only.

2. Step 2: Effect on array size

   Removing the last element reduces the array size by one.

3. Final Answer:

   The last element is removed and the array size decreases by one. -> Option D

4. Quick Check:

   Delete end element = size - 1 [OK]

Hint: Deleting at end removes last element and shrinks array [OK]

Common Mistakes:

• Thinking the first element is removed
• Assuming array size stays the same
• Believing elements shift right

2. Which of the following C# code snippets correctly deletes the last element from an array named arr?

easy

A. arr.Delete(arr.Length);

B. arr.RemoveAt(arr.Length - 1);

C. arr = arr.Take(arr.Length - 1).ToArray();

D. arr.Pop();

Solution

1. Step 1: Check valid array deletion methods

   Arrays in C# are fixed size; to delete last element, create new array excluding last.

2. Step 2: Analyze options

   arr = arr.Take(arr.Length - 1).ToArray(); uses LINQ Take to get all but last element and converts to array, which is correct.

3. Final Answer:

   arr = arr.Take(arr.Length - 1).ToArray(); -> Option C

4. Quick Check:

   Use Take and ToArray to delete last element [OK]

Hint: Use Take(arr.Length - 1).ToArray() to remove last element [OK]

Common Mistakes:

• Using RemoveAt on array (only for List)
• Calling Pop() on array (not supported)
• Using invalid Delete method

3. What is the output of the following C# code?

int[] arr = {10, 20, 30, 40};
arr = arr.Take(arr.Length - 1).ToArray();
Console.WriteLine(string.Join(", ", arr));

medium

A. 10, 20, 30

B. 10, 20, 30, 40

C. 20, 30, 40

D. 10, 20, 40

Solution

1. Step 1: Understand the Take method

   arr.Take(arr.Length - 1) takes first 3 elements: 10, 20, 30.

2. Step 2: Convert to array and print

   After conversion, arr has 3 elements: 10, 20, 30, printed with commas.

3. Final Answer:

   10, 20, 30 -> Option A

4. Quick Check:

   Take length-1 elements = 10, 20, 30 [OK]

Hint: Take length-1 elements to remove last [OK]

Common Mistakes:

• Printing original array without deletion
• Confusing which elements are taken
• Assuming last element remains

4. Identify the error in this C# code that tries to delete the last element of an array:

int[] arr = {1, 2, 3, 4};
arr.RemoveAt(arr.Length - 1);

medium

A. Arrays do not have RemoveAt method; use List instead.

B. RemoveAt index should be 0, not arr.Length - 1.

C. RemoveAt removes first element, not last.

D. RemoveAt requires two parameters.

Solution

1. Step 1: Check array methods

   Arrays in C# do not support RemoveAt; it's a List method.

2. Step 2: Correct approach

   To delete last element from array, create new array or use List instead.

3. Final Answer:

   Arrays do not have RemoveAt method; use List instead. -> Option A

4. Quick Check:

   RemoveAt not in array, only List [OK]

Hint: RemoveAt works on List, not array [OK]

Common Mistakes:

• Trying RemoveAt on array
• Wrong index for RemoveAt
• Assuming RemoveAt needs two parameters

5. You have an array int[] arr = {5, 10, 15, 20, 25};. Write C# code to delete the last two elements and print the resulting array.

hard

A. arr = arr.Take(2).ToArray(); Console.WriteLine(string.Join(", ", arr));

B. arr = arr.Take(arr.Length - 2).ToArray(); Console.WriteLine(string.Join(", ", arr));

C. arr = arr.Skip(2).ToArray(); Console.WriteLine(string.Join(", ", arr));

D. arr.RemoveRange(arr.Length - 2, 2); Console.WriteLine(string.Join(", ", arr));

Solution

1. Step 1: Remove last two elements using Take

   Take(arr.Length - 2) keeps first 3 elements: 5, 10, 15.

2. Step 2: Convert to array and print

   Convert to array and print elements separated by commas.

3. Final Answer:

   arr = arr.Take(arr.Length - 2).ToArray(); Console.WriteLine(string.Join(", ", arr)); -> Option B

4. Quick Check:

   Take length-2 elements = 5, 10, 15 [OK]

Hint: Use Take(length - 2) to remove last two elements [OK]

Common Mistakes:

• Using RemoveRange on array (only for List)
• Using Skip to remove from start instead of end
• Taking wrong number of elements